The present invention pertains to the suppression of undesirable fugitive emissions or fume that is prevalent in the pouring of molten metal, particularly that of iron or steel.
When molten metals are poured from one container to another in various metal production processes the pouring is accompanied by the emission from the receiving container of large amounts of fume. One typical example is the transfer of refined steel into a receiving ladle upon tapping of the converter or steelmaking furnace. The generation of such fugitive emissions constitutes a serious atmospheric pollution problem, the abatement of which represents a significant part of the cost of performing many metallurgical processes.
Much effort and expense has been expended in the development of emission control systems that are effective to maintain the volume of fugitive emissions associated with molten metal pouring within acceptable limits. Past efforts include the development of various forms of air or gas curtains and fume exhaust equipment adapted to isolate the affected region of the plant and to conduct the undesirable effluent to treating apparatus prior to its discharge into the atmosphere. Such prior art developments are exemplified by U.S. Pat. Nos. 3,396,954, granted Aug. 13, 1968 to Krogsrud; 3,834,293, granted Sept. 10, 1974 to Danieli; and 3,994,210, granted Nov. 24, 1975 to Davis. These systems all rely on the capture and disposal of the fugitive fume and, while being effective to a limited degree in solving the concerned problem, entail significant capital expenditure to install and are costly to operate.
Japanese Pat. No. 53-6602, granted Mar. 9, 1978 to Nippon Steel Corporation, on the other hand, teaches an emission control system in which fugitive fume is sought to be suppressed by blanketing the molten bath with an inert gas, such as steam or nitrogen, to retard metallic oxide formation. A yet more effective system for suppressing fume is described in U.S. patent application Ser. No. 286,395 filed July 23, 1981 by Ball et al. and assigned to the assignee herein, wherein a mixture of water and inert gas is injected into the receiver over the molten bath for fume suppression. This latter system, although most effective in suppressing fume, is not without some attendant disadvantages. For example, unless appropriate precautions are taken, the presence of steam in the vicinity of a molten bath is potentially dangerous due to the possibility of condensate leakage into the bath and the creation of an explosive condition.
Another problem with fume suppression by steam blanketing arises due to the fact that steam, being at a significantly lower temperature than the molten bath, tends to chill the bath thereby resulting in the release of free carbon flakes, termed "kish", that, unless captured, permeate the atmosphere surrounding the receiver.
Still another problem attendant with the use of steam as a fume suppressant is that water vapor can have an adverse metallurgical effect on certain products produced from the affected metal. Specifically, it has been determined that products having thick sections, such as heavy structural members, may retain residual amounts of hydrogen acquired from the application of steam to the bath for fume suppressing purposes.
It is to the amelioration of the above problems and to the development of a more effective emission control system for molten metal teeming operations that the present invention is directed.